Two-step extraction chromatography separation of 161Tb from 160Gd-enriched irradiated target material and verification of the [161Tb]TbCl3 suitability for radiolabelling

Terbium-161 (T_1/2 = 6.89 d) is a low-energy β^- emitter (β^-_max 460 and 522 keV). It also emits γ radiation (25.6, 48.9, and 74.6 keV). Tb-161 decays to stable ¹⁶¹Dy. These physical properties make it similar to ¹⁷⁷Lu (T_1/2 = 6.65 d). However, ¹⁶¹Tb also emits a significant amount of conversion and Auger electrons, which are expected to provide a more pronounced therapeutic effect than ¹⁷⁷Lu. Tb-161 can be produced in nuclear reactors in ¹⁶⁰Gd(n,γ)¹⁶¹Gd →¹⁶¹Tb nuclear reaction and separation of Tb-161 from the target material is required. Herein, we present the results of Tb-161 separation after irradiation of enriched gadolinium-160 in the MARIA Research Reactor (NCBJ, Poland). The separation of Tb-161 from a gadolinium target was optimized in a two-step solid phase extraction chromatography, first on LN2 and then on DGA resin. After dissolving the target in 3 M HCl, the solution was loaded on the LN2 column, and Tb-161 was eluted with a gradient from 0.25M to 1M HNO₃. The eluted Tb-161 nitrate was loaded on the DGA column and eluted with diluted HCl. Quality control tests included radionuclidic, chemical and radiochemical purity. In addition, the effective specific activity and the apparent molar activity were assessed using the DTPA and DOTA-TATE radiolabeling tests, respectively. High recovery efficiency of Tb-161 from LN2 resin (>98 %) was achieved.The radiolabelling efficiency of the DOTA-TATE was over 98 % at ¹⁶¹Tb:peptide molar ratio of 1:5.